In general, a light emitting diode (LED) is a device utilizing a phenomenon in which minority carriers (electrons or holes) injected by means of a p-n junction structure of a semiconductor are produced, and light is emitted due to recombination of the carriers. Conventionally, colors of light emitted by a light emitting diode are only red and green, and thus, the conventional light emitting diode has its use limited to a display device.
With the development of technology, however, light emission is allowed in various ranges of wavelength, in addition to blue light emission. Thus, a light emitting diode has begun to be used in a variety of fields. In particular, as white light emission is realized, the use of the light emitting diode is expanded to an illumination device as well as a backlight for a liquid crystal display.
However, since the direction of light emitted by a light emitting diode is random, the light should be induced in a desired direction to be used as an illumination device and a backlight. To induce light in the prior art, as shown in FIG. 1, a luminescent chip 11 is mounted on a substrate 10, molding is performed to form a convex lens 12 over the luminescent chip 11, and a pattern 13 for diffused reflection is formed on the surface of the convex lens 12 so that light can be spread widely. As shown in FIG. 2, reflection cups 14 are formed at both sides of the luminescent chip 11 to enhance focusing of light. Since the aforementioned luminescent device mainly emits light forward rather than sideward, there is a problem in that it is difficult to apply the luminescent device to a backlight which should widely emit light sideward.
Accordingly, studies on development of a device capable of emitting light in side directions of a lens have been actively conducted using the total internal reflection (TIR) property of light. Conventional lenses using TIR are disclosed in U.S. Pat. Nos. 6,679,621, 6,607,286 and 6,598,998. In the patents, a lens comprises a total reflection surface which is formed on the lens and has a predetermined slope, and a plurality of refractive surfaces which have different slopes and through which light reflected by the total reflection surface is emitted to the outside. Since the conventional lens has the plurality of refractive surfaces formed on right and left sides of the total reflection surface, there is a problem in that a process of fabricating the lens is complicated and fabricating costs increase. That is, there are the following problems: if a lens is fabricated using a mold, upper and lower mold parts and right and left mold parts are required; and if a lens is fabricated by means of a casting or grinding method, it cannot be easily fabricated in view of its shape.